218 research outputs found
Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum
Statistical -decay from highly excited states is determined by the
nuclear level density (NLD) and the -ray strength function
(SF). These average quantities have been measured for several nuclei
using the Oslo method. For the first time, we exploit the NLD and SF to
evaluate the -width in the energy region below the neutron binding
energy, often called the quasi-continuum region. The lifetimes of states in the
quasi-continuum are important benchmarks for a theoretical description of
nuclear structure and dynamics at high temperature. The lifetimes may also have
impact on reaction rates for the rapid neutron-capture process, now
demonstrated to take place in neutron star mergers.Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figure
Scissors resonance in the quasi-continuum of Th, Pa and U isotopes
The gamma-ray strength function in the quasi-continuum has been measured for
231-233Th, 232,233Pa and 237-239U using the Oslo method. All eight nuclei show
a pronounced increase in gamma strength at omega_SR approx 2.4 MeV, which is
interpreted as the low-energy M1 scissors resonance (SR). The total strength is
found to be B_SR = 9-11 mu_N^2 when integrated over the 1 - 4 MeV gamma-energy
region. The SR displays a double-hump structure that is theoretically not
understood. Our results are compared with data from (gamma, gamma') experiments
and theoretical sum-rule estimates for a nuclear rigid-body moment of inertia.Comment: 11 pages, 9 figure
Completing the nuclear reaction puzzle of the nucleosynthesis of 92Mo
One of the greatest questions for modern physics to address is how elements
heavier than iron are created in extreme, astrophysical environments. A
particularly challenging part of that question is the creation of the so-called
p-nuclei, which are believed to be mainly produced in some types of supernovae.
The lack of needed nuclear data presents an obstacle in nailing down the
precise site and astrophysical conditions. In this work, we present for the
first time measurements on the nuclear level density and average strength
function of Mo. State-of-the-art p-process calculations systematically
underestimate the observed solar abundance of this isotope. Our data provide
stringent constraints on the NbMo reaction rate,
which is the last unmeasured reaction in the nucleosynthesis puzzle of
Mo. Based on our results, we conclude that the Mo abundance
anomaly is not due to the nuclear physics input to astrophysical model
calculations.Comment: Submitted to PR
Statistical properties of Pu, and Pu(n,) cross section calculation
The level density and gamma-ray strength function (gammaSF) of 243Pu have
been measured in the quasi-continuum using the Oslo method. Excited states in
243Pu were populated using the 242Pu(d,p) reaction. The level density closely
follows the constant-temperature level density formula for excitation energies
above the pairing gap. The gammaSF displays a double-humped resonance at low
energy as also seen in previous investigations of actinide isotopes. The
structure is interpreted as the scissors resonance and has a centroid of
omega_{SR}=2.42(5)MeV and a total strength of B_{SR}=10.1(15)mu_N^2, which is
in excellent agreement with sum-rule estimates. The measured level density and
gammaSF were used to calculate the 242Pu(n,gamma) cross section in a neutron
energy range for which there were previously no measured data.Comment: 9 pages, 8 figure
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